This invention relates to an improved process for the preparation of 5-chloroisophthaloyl chloride. The product is useful as a chemical intermediate in the preparation of various products, especially agricultural chemicals, such as herbicides and the like.
U.S. Pat. No. 3,869,510 to Gelfand discloses a process for the preparation of 5-chloroisophthaloyl chloride by reaction of isophthaloyl chloride with chlorine gas in the presence of molybdenum pentachloride catalyst at a temperature of about 227.degree. C. The 5-chloroisophthaloyl chloride product is shown to be useful in the further synthesis of 3,5-dichlorobenzoyl chloride which in turn is disclosed as a useful intermediate in the further preparation of various biologically active compounds.
U.S. Pat. No. 3,821,310 to Brunetti et al discloses the use of 5-chloroisophthaloyl chloride as an intermediate in the synthesis of 1,3-bis-(2'-hydroxy-4'-methoxy-benzoyl)-5-chlorobenzene, a product useful as a light stabilizer in polymeric materials.
Although 5-chloroisophthaloyl chloride has been known to be a useful intermediate for a number of years, the processes for its production have been found to present difficulties, especially with respect to the purity of the product. In particular, prior art processes have been found to result in the simultaneous formation of undesired isomers and over-chlorinated products, most especially the undesired isomer 4-chloroisophthaloyl chloride, and over-chlorinated products including for example, dichloroisophthaloyl chlorides. The production of isomers and over-chlorinated products results in the necessity of additional separation steps, and disposal of undesired products with a resultant economic disadvantage. The 4-chloroisophthaloyl chloride, having a boiling point close to that of 5-chloroisophthaloyl chloride, is particularly troublesome to separate.
It is an object of this invention to provide an improved process for the preparation of 5-chloroisophthaloyl chloride having improved selectivity, specifically with the enhancement of production of 5chloroisophthaloyl chloride in preference to 4-chloroisophthaloyl chloride at relatively low temperatures and with minimal overchlorination. It is a further object of this invention to provide a process whereby 5-chloroisophthaloyl chloride may be prepared at an expeditious rate while realizing the desired selectivity.